Every year, as temperatures soar during the scorching summer months, the searing heat experienced in New York City is increasingly exacerbated by climate change and will also be amplified by another factor: the city itself. 

The city’s densely packed buildings and dark pavement absorb and radiate heat from the sun, trapping heat and making the city feel like an oven. This phenomenon is known as the “heat island effect,” and our concrete jungle is the third-most intense heat island in the U.S., behind only Newark, N.J., and New Orleans, Louisiana. 

“New York is definitely one of the epicenters for heat,” said Vivek Shandas, professor of climate adaptation and founder and director of the Sustaining Urban Places Research Lab at Portland State University. “Unfortunately, what we’ve done in our cities is really build them out so much that we’ve eliminated a lot of the green space and trees…and very disproportionately.”

This phenomenon has an impact on some parts of the city more than others. Here’s why it’s important to understand to stay safe this summer. 

Why is the heat island effect dangerous?

Rising temperatures due to climate change are creating conditions for more extreme floods, hurricanes, and storms, but extreme heat is the deadliest of them. On average, more than 67,000 people in the United States end up in emergency rooms every year due to heat-related health issues. 

In New York City, the number of emergency room visits for heat have gone back up since they dipped in the summer of 2020. There were 370 heat-exacerbated fatalities in the city in 2021, according to the New York City Department of Health and Mental Hygiene (DOHMH). 

Heat mortality rates are more than twice as high among Black New Yorkers, who, alongside poor and marginalized communities, tend to experience record high temperatures in their neighborhoods and the least shielding from heat. Even though more than 90% of New Yorkers have air conditioning, 81% of people dying from extreme heat have no A/C at home.

“It’s gotten to a point where it’s actually killing more people every year,” Shandas said. “And it’s often…Black and brown communities, older communities, communities that have been historically more marginalized that are facing the brunt of the impacts from urban heat.”

Mapping the hottest neighborhoods

Trapped heat is made worse by a lack of trees and greenery, and building designs that restrict air flow, creating neighborhoods with hot and stagnant air. 

High disinvestment in neighborhoods like Harlem, Hunts Point, and East Flatbush—linked to historical practices like redlining and redirecting public infrastructure resources to wealthier neighborhoods—intensifies the heat island effect in those areas. 

In 2021, Harlem was nearly 10 degrees hotter than other neighborhoods surrounding Central Park. To make matters worse, the density of cooling centers—designated public facilities like libraries and senior centers that were open during heat emergencies for New Yorkers to cool down—is lower in some of the most heat-vulnerable neighborhoods. 

Last summer, Shandas and a team at the New York Environmental Justice Alliance worked on a project to measure air temperatures all around New York, expanding on a project from the previous year focused on the Bronx. Community volunteers fanned across the city on foot and on bicycles, collecting up-to-the-minute temperature changes in different neighborhoods of the city.

“We were able to show, at very high resolution, how areas that have been historically kind of disinvested,” Shandas said. He said their research found that Harlem and the Bronx were  consistently 10 degrees higher than some highly built-out areas in lower Manhattan.

Solutions that beat the heat

The U.S. Environmental Protection Agency (EPA) recommends a few approaches to combat heat island effect: creating rooftop gardens, painting roofs in light colors, and putting cool pavements on the street that reflect the heat.

Trees play a critical role in mitigating the effect. A European study recently published in the Lancet found that 30% of deaths caused by the heat island effect could be prevented with more tree cover. Trees provide shade that can significantly decrease temperatures and release water into the atmosphere, cooling the air. Shandas called trees “the original air conditioning systems” for society.

Trees also offer energy-saving benefits, such as lowering electric bills and preventing the evaporation of harmful organic compounds from gas tanks in shaded parking lots. Every year, through June 30, New York City residents can apply to have a tree planted on their street. But as resilient as trees are, they require lots of care—pruning, watering—to thrive and provide those cooling benefits in cities. 

Despite new federal investment in environmental justice remedies, lots of neighborhood cooling efforts rely on community members volunteering their time to bring about these changes and check in on their neighbors. 

Staying cool this summer 

To stay safe during the summer, it is important to recognize the symptoms of heat-related illnesses and take prompt action. 

Heat stress is the mildest form of heat-related illness and typically presents with symptoms such as heavy sweating, fatigue, muscle cramps, dizziness, and headache. If not addressed, it can progress to heat exhaustion, characterized by increased body temperature, rapid heartbeat, nausea, weakness, and clammy skin. Heat exhaustion requires immediate attention to prevent it from advancing to heat stroke.

“I always people tell that heat distress can happen in the young and old, and sometimes it comes on very quickly and you’re in the middle before you realize it,” said Lauren Smalls-Mantey, a senior environmental systems scientist studying extreme heat for the New York City Department of Health and Mental Hygiene (DOHMH). 

Even when temperatures drop at night, prolonged periods of hot weather can still cause heat distress, Smalls-Mantey added. This is because the body hasn’t had a chance to recover from high daytime temperatures. At night, indoor temperatures in homes without A/C “can be higher than the outdoor temperature because buildings tend to retain heat after prolonged periods of hot weather,” she said. 

The CDC recommends staying hydrated by drinking water regularly, especially in hot weather or when engaging in physical activities. Wearing lightweight, loose-fitting, and breathable clothing, and avoiding direct sun exposure during peak hours in the early afternoons is best for the hotter summer days. Take frequent breaks in shaded or air-conditioned areas and be mindful of the signs of heat-related illness in oneself and others.

Prevention is key to avoiding getting sick in the heat. If staying cool at home isn’t possible during a heat emergency, call 311 to find the nearest cooling center. 

“When you see these heat warnings, pay attention and be careful,” said Smalls-Mantey. “Hydrate, make sure you know your options.”

The federally funded, state-administered Home Energy Assistance Program (HEAP) of the New York City Human Resources Administration (HRA) provides a limited number of air conditioning units on a first-come, first-served basis as part of the summer Cooling Assistance Component. Eligible low-income residents can apply online or in person at one of HRA’s benefits access centers, which also can be found by calling 311. 

Until enough adaptations are in place to create equitably cooler cities, climbing temperatures will continue to disrupt lives. Smalls-Mantey said that solving for extreme heat requires not just inter-agency cooperation and funding, but also community education to be effective. 

“We have to do education toward heat safety,” she said.